This application claims the benefit of Korean Patent Application No. 1999-16742, filed on May 11, 1999, under 35 U.S.C. xc2xa7 119, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a reflective liquid crystal display device, and more particularly to a reflective liquid crystal display device having an auxiliary light source.
2. Description of Related Art
In general, liquid crystal display devices are divided into transmissive liquid crystal display devices and reflective liquid crystal display devices depending on whether an internal or an external light source is used.
While the transmissive liquid crystal display device uses an internal light source such as a backlight, the reflective liquid crystal display device uses ambient light and thus is affected by the surroundings. For example, the brightness of ambient light in an office differs largely from that in the outdoors. Also, even in the same location, the brightness of outer light depends on the time of day (e.g., noon or dusk). Hence, it is desirable for an auxiliary light source to be mounted on the reflective liquid crystal display device to remove such dependence on the ambient light.
FIG. 1 is a cross-sectional view illustrating, schematically, the principle of an auxiliary light source of a prior art reflective liquid crystal display device. The auxiliary light source mounted on the display device body 4 has a lamp 1, a lamp reflector 2, and a waveguide plate 3. The display device body 4 includes a reflector (not shown), for reflecting incident light from the light source or a natural light.
A reflective LCD device as described generally utilizes the natural light as a light source, but the auxiliary light source is operated when it is dark or in dark surroundings. First, light is emitted from the lamp 1 and the emitted light is directed in a direction via the lamp reflector 2. Then, the collected light is reflected upwards and downwards while passing through the light waveguide plate 3, due to the structure of the waveguide plate 3. Thus, only the light incident within a determined range of angles with the vertical direction is transmitted upward, and the remainder light is reflected downward.
Downward light is incident to the body 4 of the reflective liquid crystal display device and is reflected by the reflective electrode or reflector (not illustrated) in the body 4. The reflected light passes through the light waveguide plate 3 and then is viewed as information by the user.
An example of the above described display with an auxiliary light source is a personal portable terminal (model name: Zaurus MI-310) of Sharp Kabushiki Kaisha, in which the auxiliary light source is fixed.
As described above, the conventional reflective liquid crystal display device utilizes an auxiliary light source for light supply when it is dark, thereby improving the display characteristics of the reflective LCD device. However, even when the auxiliary device is not used, the ambient light or natural light must still pass through the auxiliary device, and thus the contrast ratio of the LCD device is decreased by the reflected light on the surface of the auxiliary light source. Also, the auxiliary device is inconvenient to carry due to its size and weight. Moreover, some users may not want such an auxiliary light source. Therefore, there has been an increasing need for a detachable auxiliary light source that may be substituted for the conventional auxiliary light source.
An object of this invention is to provide a reflective liquid crystal display device with an auxiliary light source that is capable of being detached according to the preference of the user.
In order to achieve the object, one embodiment of the invention provides a reflective liquid crystal display device having a body case containing a reflective liquid crystal display; and an auxiliary light source for supplying light to the display, the auxiliary light source being attachable to and removable from the body case by a user of the device.
Another embodiment of the invention provides a reflective liquid crystal display device having a reflective liquid crystal display; and a body case to protect the display, including engaging structure to selectively engage an auxiliary light source with the body case, and electric connection structure to electrically connect the body case and the auxiliary light source.
Another embodiment of the invention provides a removable auxiliary light source for use with a reflective liquid crystal display device, including: an auxiliary light source for supplying light to the display device, including engaging structure to selectively engage the auxiliary light source with a body of the display device, and electric connection structure to electrically connect the body and the auxiliary light source.